1. Field of the Invention
The present invention relates generally to a portable internet analyzer having a handover test function and, more particularly, to a portable Internet analyzer having a handover test function, which enables a handover test function to be effectively performed on a Portable Subscriber Station (PSS) using a single portable Internet analyzer.
2. Description of the Related Art
Currently, methods of wirelessly accessing the Internet include a method of accessing the Internet via a mobile telephone network based on a Wireless Application Protocol (WAP) or Wireless Internet Platform for Interoperability (WIPI) platform, and a method of accessing the Internet via a public wireless Local Area Network (LAN) or an Access Point (AP). However, the method using a mobile telephone network has fundamental limitations on use as a universal Internet access method due to the limited screen size, the limited input interface, and a billing system based on a measured rate system. Meanwhile, the method using a wireless LAN has fundamental problems in that it can only be used within a range having a radius of tens of meters around an AP, and in that it also realizes poor mobility. In order to overcome such problems, ‘portable Internet service’ (mobile WiMAX, or WiBro, which is a subset of mobile WiMAX and a Korean portable Internet standard) has been proposed as wireless Internet service capable of enabling high-speed Internet access at ADSL-level quality and cost, either when at rest or in intermediate-speed motion.
FIG. 1 is a diagram illustrating a method of allocating resources along a time axis and a frequency axis in Orthogonal Frequency Division Multiple Access (OFDMA). In general communication systems, since radio resources, that is, time and frequency, are limited, they must be allocated to a plurality of PSS users and used by them. Meanwhile, unlike existing CDMA-based systems and Wireless LAN (WLAN) systems, portable Internet systems employ OFDMA, in which a two-dimensional resource region, defined by the time axis and the frequency axis, is allocated to respective PSSs, as shown in FIG. 1.
FIG. 2 is a diagram showing the MAP structure of a portable Internet system. As shown in FIG. 2, in the portable Internet system, a plurality of pieces of data using the same channel coding method and modulation method is sent in a batch in order to improve efficiency. A set of data regions using the same channel coding method and modulation method is referred to as a “burst.” The location and size information of each burst can be seen from the MAP information of a frame, as shown in FIG. 2. Here, the term ‘frame’ refers to a structured data sequence having a fixed duration, which is used in the Physical Layer (PHY) standard. A single frame may include both of a Downlink (hereinafter abbreviated as “DL”; a link from a Radio Access Station (PAS) to a PSS) sub-frame and an Uplink (hereinafter abbreviated as “UL”; a link from a PSS to an RAS) sub-frame.
Since the portable Internet system employs Time Division Duplexing (TDD), in which UL transmission and DL transmission share the same frequency but are performed at different times, essential information, including the length of a single frame and the ratio of a DL section to a UL section, is provided via MAP information. In order to dynamically allocate resources to PSSs, an RAS may send different MAPs through each frame. In this case, a MAP may be divided into DL_MAP, containing DL transmission information, and UL_MAP, containing UL resource access authority. Here, DL_MAP can be defined as a Media Access Control (MAC) layer message that defines the symbol offset and sub-channel offset of a burst divided and multiplexed along the subchannel and time axes on a downlink by an RAS, and the numbers of symbols and sub-channels, that is, allocated resources. Furthermore, a preamble, which is defined uniquely, is present in the first symbol of the DL subframe, and the preamble includes cell Identification (ID) information and segment information.
Meanwhile, the portable Internet system supports a handover function for preventing the connection of a PSS from being terminated in the case where a PSS moves from a wireless interface, provided by an RAS, to a wireless interface, provided by another RAS, as in a typical mobile communication system. The portable Internet standard provides for an article that conducts the test of whether a PSS effectively performs a handover. Handover is classified as break-before-make handover, in which service from a target base station (hereinafter simply abbreviated as a ‘target BS’) starts to be provided after connection with an existing serving base station (hereinafter simply abbreviated as a ‘serving BS’) has been released, or as make-before-break handover, in which service from a target BS starts to be provided before connection with an existing serving BS is released. Here, the ‘serving BS’ is a base station with which a PSS has recently registered during initial network entry or handover, and the ‘target BS’ is a base station with which a PSS will register at the end of handover.
Meanwhile, there may be a method of performing a test in an environment that is identical to an actual portable Internet environment with the assistance of a certain serving BS and a certain target BS in order to test the performance of handover on a PSS. This method has a problem in that it is impossible in practice to obtain assistance from an RAS from the point of view of the maintenance and management of RAS equipment. Additionally, there may be another method of performing a test indoors using two portable Internet analyzers. This method also has problems in that two portable Internet analyzers must be used, so that high equipment construction costs are incurred and the establishment of UL and DL synchronization and integrated control of the two analyzers are somewhat complicated.